Structural body formed by friction stir welding and having protrusion at the weld provided prior to the welding

ABSTRACT

Disclosed is a friction stir welding technique which avoids occurrence of a dent, in adjoining region, extending to a level beneath the joined surfaces, structural body formed. At end portions of the frame members to be joined, at the joining region, thickened parts which project toward the rotary body joining tool are provided. The rotary body joining tool has a small-diameter tip portion and a larger diameter portion. The rotary body joining tool is inserted in the thickened parts. In a state where the rotary body joining tool has been inserted small-diameter tip end first, to a level where the larger diameter portion of the rotary body joining tool overlaps the thickened part but does not extend below the upper surface of the non-thickened surfaces of the members joined, the rotary body is rotated and moved along the joining region.

[0001] This application is a Divisional application of application Ser.No. 09/025,070, filed Feb. 17, 1998, the contents of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a friction stir welding methodsuitable for use in a joining of members of various materials,including, for example, an aluminum alloy member, etc.

[0003] A friction stir welding method is a method in which by rotating around-shaped rod (a rotary body) inserted in a joining region betweentwo members (e.g., but not limiting, two metal bodies, such as two Albodies), and further by moving the rotary body along a joining line, thetwo bodies at the joining region are heated, and material thereofsoftened and plastically fluidized and thus the two bodies aresolid-phase joined, e.g., are welded together at the joining region.

[0004] Conventionally, the rotary body comprises a small diameterportion which is inserted in the joining region and a large diameterportion which is positioned outside the joining region. The smalldiameter portion and the large diameter portion are positioned on thesame axis. A side of the large diameter portion is rotated, whereby boththe large and small diameter portions are rotated. A boundary portionbetween the small diameter portion and the large diameter portion can beinserted a little into the joining region. A joining according to thefriction stir welding method can be applied to an abutting portion andan overlapping portion.

[0005] The above-stated prior technique is disclosed, for example, inJapanese patent announcement laid-open publication No. Hei 7-505090 (EP0615480 B1); Dawes, “An Introduction to Friction Stir Welding and ItsDevelopment”, in Welding & Metal Fabrication (January 1995), pages 13,14 and 16; and by U.S. patent application Ser. No. 08/820,231, filedMar. 18, 1997, the contents of which are incorporated herein byreference in their entirety.

[0006] This prior technique is also described in the article by T.Shinoda and Y. Kondoh, “324 Butt Welding of Plate Using Friction StirWelding; Method Study of Friction Stir Welding”, Welding Associate JapanLecture Meeting Outline, No. 56 (April 1995), pages 208 and 209. Thisarticle discloses a rotary body (rotary tool) made of stainless steel,members to be welded (joined) made of pure aluminum (A1100), and themembers to be welded having a plate thickness of 6 mm. The rotary bodyhas a large diameter portion with a diameter of 20 mm, and a smalldiameter portion (cylindrical) with a diameter of 6 mm and a length(axially) of 5 mm. In operation, the rotary body rotates at 1000-2500rpm, and moves along the two members to be welded at a speed of 1.0-8.0mm/s.

[0007] In the article described in the foregoing paragraph, the membersto be joined are made of aluminum. Alloys of aluminum are also suitablefor welding by friction stir welding; other metals studied for weldingby friction stir welding include copper, titanium and stainless steel.EP 0615480 B1, referred to previously herein, discloses friction stirwelding of plastic (e.g., thermoplastic) materials. All of thesematerials can be welded by the process of the present invention.

SUMMARY OF THE INVENTION

[0008] According to various experiments of the friction stir weldingmethod, a part of an upper face of a joining region of two members ismachined as chips, by a rotation of the large diameter portion of therotary body, and a dent is caused in the upper face of the joiningregion. At both sides of the dent, a thickened part is caused accordingto plastic deformation of the members.

[0009] It is easy to delete the thickened part; however, correcting forthe dent needs a putty working, etc., and as a result a highmanufacturing cost is caused.

[0010] Further, in a case where before the joining working a gap existsbetween end faces of the abutting faces of the two members, a defaultsuch as a dent, etc., is generated at the joining region. As a result, alowering in strength is caused, and particularly in a large-scaleconstruction it invites a problem. The larger the members, the more amanagement in the above-stated gap becomes difficult (i.e., the more thegap occurs); accordingly, the dent becomes large, and, moreover, adefault is generated easily.

[0011] In a case where the joining region is covered by another member,for example, the existence of the dent is not as much a problem, andthere is no problem except for the strength problem (which, of course,can be a serious problem itself). However, in a side face, etc., of acar body of cars (e.g., railroad cars), it is necessary to remove thedent from a viewpoint of an outward appearance. Further, even in a casewhere the dent is not visible, the dent becomes a problem from an aspectof the performance (e.g., strength of the weld).

[0012] An object of the present invention is to prevent generation of adent in a joining region when joining two members (e.g., but not limitedto, two metal members, such as of aluminum alloy) by a friction stirwelding method.

[0013] Another object of the present invention is to provide members, tobe joined by friction stir welding, which avoid a dent in the joiningregion between the joined members.

[0014] Still another object of the present invention is to provide afriction stir welding method, and product manufactured thereby, wherebya dent can be avoided in the joining region between joined members,where the members joined are abutting each other before being joined oreven where there is a small gap between the members before they arejoined (but the members are adjacent each other).

[0015] The above-stated objects can be attained by a provision where atleast one of the members to be joined has a thickened part, in crosssection, at the joining region thereof with another member, thethickened part protruding toward the rotary body used to perform thefriction stir welding. The rotary body has large and small diameterportions, e.g., made of a material or materials harder than the materialof the members to be welded, the small diameter portion first beinginserted in the joining region of the members to be joined, during thejoining. The members to be joined are positioned adjacent each other,with the thickened part of one member being positioned adjacent theother member to be joined thereto by welding. Where both members havethickened parts, the thickened parts can be positioned adjacent eachother in the joining (joint-forming) region, or only one thickened partneed be positioned in the joint-forming region. The rotary body is thencaused to enter between the two members, in the joining region, with thesmall diameter portion of the rotary body being inserted into thejoint-forming region of the two members and the large diameter portionof the rotary body extending into the thickened part (but not below thethickened part). The rotary body is then moved along the members to bewelded, in the joining region, with the rotary body inserted asdescribed in the previous sentence to perform the friction stir welding.Due to provision of the thickened part, at the joint-forming region, adent (depressed region) at the weld region, in the joined members, canbe avoided. By positioning the rotary body such that the large-diameterportion thereof is inserted into the thickened part (overlaps with thethickened part), an excellent weld is achieved, while avoiding a dent inthe welded joint. Advantageously, the large-diameter portion of therotary body does not extend below the protruding portion of thethickened part, while moving the rotary body to perform the frictionstir welding.

[0016] The thickened part of the member can be an integral part of themember, and, e.g., extends to the edge (of the member) which is to bepositioned adjacent another member to which the member is to be welded.

[0017] Preferably, the protruding portion has a side, furthest from theweld location, which, in cross section, is sloped (e.g., makes an acuteangle of less than 90° with the plane of the surface of the member(other than the protruding portion); see θ in FIG. 4). Desirably, thisside furthest from the weld location makes an angle of 15°-60°,preferably 30°, with the plane of the surface of the member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a longitudinal cross-sectional view showing a part ofone embodiment according to the present invention.

[0019]FIG. 2 is a longitudinal cross-sectional view showing a stateafter a friction stir welding of the structure of FIG. 1.

[0020]FIG. 3 is a longitudinal cross-sectional view showing a state inwhich after a friction stir welding of the structure of FIG. 1 has beencarried out, a finishing process is carried out on one side.

[0021]FIG. 4 is a view for explaining dimensions.

[0022]FIG. 5 is a perspective view showing a car body of a railway car.

[0023]FIG. 6 is a longitudinal cross-sectional view showing a part ofanother embodiment according to the present invention.

[0024]FIG. 7 is a lateral cross-sectional view showing a joining regionof another embodiment according to the present invention.

[0025]FIG. 8A is a longitudinal cross-sectional view showing a joiningapparatus of one embodiment according to the present invention.

[0026]FIG. 8B is a longitudinal cross-sectional view of part of anotherembodiment according to the present invention.

[0027]FIG. 8C is a left-side view of FIG. 8B.

[0028]FIG. 8D is a longitudinal cross-sectional view of a part of afurther embodiment according to the present invention.

[0029]FIG. 9 is a longitudinal cross-sectional view showing a joiningregion of a further embodiment according to the present invention.

[0030]FIG. 10 is a longitudinal cross-sectional view showing a weldedstructure after a friction stir welding of the structure of FIG. 9.

[0031]FIG. 11 is a longitudinal cross-sectional view showing theresulting structure after a thicker part of the structure in FIG. 10 isfinished smoothly.

[0032]FIG. 12 is a longitudinal cross-sectional view of a joining regionof another embodiment according to the present invention.

[0033]FIG. 13 is a longitudinal cross-sectional view showing theresulting structure after a friction stir welding of the structure shownin FIG. 12.

[0034]FIG. 14 is a longitudinal cross-sectional view showing theresulting structure after a thicker part of the structure shown in FIG.13 is finished smoothly.

[0035]FIG. 15 is a longitudinal cross-sectional view of a joining regionof another embodiment according to the present invention.

[0036]FIG. 16 is a longitudinal cross-sectional view showing theresulting structure after a friction stir welding of the structure shownin FIG. 15.

[0037]FIG. 17 is a front view of a side structure body of a railwayvehicle.

[0038]FIG. 18 is a cross-sectional view taken along the line XVIII-XVIIIof FIG. 17.

[0039]FIG. 19 is a right-side view of FIG. 18.

[0040]FIG. 20 is a longitudinal cross-sectional view of a part of afurther embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] One embodiment of the present invention, which is an applicationof the present invention for a car body of railway cars, will beexplained referring to FIGS. 1-5.

[0042] In FIG. 5, a car body of a railway car is comprised of a sideconstructive body 41, a roof constructive body 42, a floor constructivebody 43, and a constructive body 44 of an end portion at a longitudinaldirection. The side constructive body 41 is constituted by arrangingplural hollow extruded frame members (50, 60) and by joining contactingportions thereof. The joining is carried out as shown in FIG. 1.

[0043] Each of the roof constructive body 42 and the floor constructivebody 43 is constituted similarly. Connections between the sideconstructive body 42 and the roof constructive body 41 and the floorconstructive body 43 are carried out using an MIG (metal electrode inertgas) welding, etc.

[0044]FIG. 1 shows a joint portion of a hollow frame member whichconstitutes the side constructive body 41. The hollow frame members 50and 60 are extruded frame members made from an aluminum alloy, forexample. The hollow frame members 50 and 60 each comprise two plates 51,52 and 61, 62, and diagonal plates (ribs) 53 and 63 which connect theplates. The plural diagonal plates 53 and 63 are arranged with a trussshape. The inclination directions of the plates 53 and 63 arealternately.

[0045] An end portion of one hollow frame member 50 is entered into anend portion of another hollow frame member 60. A vertical plate 54 forjoining the plate 51 and the plate 52 is provided at a vicinity of theend portion of the hollow frame member 50. A reference numeral 54 is anextruded member for supporting the end portion of the hollow framemember 50.

[0046] On an extension line of a center of the thickness direction (inFIG. 1, a right and left direction) of the plate 54, the end portions ofthe members to be joined have thickened parts (protruding portions) ofthe two hollow frame members 50 and 60. Namely, an end portion (a centerof a welding region W) of each of the hollow frame members 50 and 60, atwhich the joining is performed, is thickened so as to form theprotruding portions.

[0047] The plates 51, 52 and 61, 62 are positioned nearly to the weldingregion W (see FIG. 2, for example) and are extruded and formed thick toform the thickened parts at a side of a front face (an outside in thethickness direction of the hollow frame member, or a side facing thetool for carrying out the joining working (welding), namely, a sidefacing the rotary body 70 which is a tool for friction stir welding.

[0048] The thickened parts 56 and 66 are formed respectively at the endportions of the plates 51, 52 and 61, 62. The front faces (the outerfaces) of the thickened parts 56 and 66 are connected smoothly andinclined toward the front faces (the outer faces) of the plates (thenon-thickened portions, which may be planar) 51, 52 and 61, 62. When twothickened parts 56 and 66 are aligned, then they can form a trapezoidshape illustrated in FIG. 1, although the present invention is notlimited to the aligned parts 56 and 66 forming a trapezoid shape.

[0049] The rotary bodies 70 and 70, which are the joining tools forfriction stir welding, are arranged respectively at an upper portion andat a lower portion of the joining regions of the hollow frame member.Each rotary body 70 has a small diameter round-shape rod 72 (a smallerdiameter portion) at a tip end of a large diameter round-shape rod (alarger diameter portion) 71 which acts as a base portion. The largediameter portion 71 and the small diameter portion 72 are disposed onthe same axis.

[0050] The lower side rotary body 70 is positioned downwardlysubstantially vertically below the upper side rotary body 70. The rotarybodies 70 and 70 can be separated along the joining line; however, toprevent bending of the hollow frame members 50 and 60, it is desirableto not separate the upper and lower rotary bodies a large distance inthe direction along the joining line. The material of the rotary body 70is harder than the materials of the hollow frame members 50 and 60.

[0051] By rotating the two rotary bodies 70 and 70, the small diameterportion 72 is inserted into the joining region of the hollow framemembers 50 and 60. After that, the two rotary bodies 70 and 70 are movedin the horizontal direction along the longitudinal direction of thejoining region of the hollow frame members 50 and 60. The two rotarybodies 70 and 70 are moved at the same time.

[0052] During the friction stir welding, at a side of the upper siderotary body 70, a boundary portion 73 (a substantially flat shapeportion), between the large diameter portion 71 and the small diameterportion 72 of the rotary body 70, is positioned spaced upward a little,at an upper portion 73 a (at a side of a face of an apex of thethickened parts 56 and 66 and in an inner portion of the thickened parts56 and 66), from an extension of an upper face of the general portion(the non-projecting portion) of the plates 51 and 61. That is, while thelarge diameter portion 71 of the upper side rotary body 70 extends belowthe upper face of the thickened part (e.g., is inserted into thethickened part), it does not extend below the level of thenon-projecting portion of the plates 51 and 61.

[0053] At a side of the lower side rotary body 70, the boundary portion73 between the large diameter portion 71 and the small diameter portion72 is positioned a little below an extension of a lower face of thegeneral portion (the non-projecting portion) of the plates 52 and 62(between the face side of the apex of the thickened parts 56 and 66 andin an inner portion of the thickened parts 56 and 66).

[0054] Namely, the boundary portion 73 between the large diameterportion 71 and the small diameter portion 72 is positioned at an outerside of the extension line of the face of the outer side of thenon-projecting portion of the plates 51 and 52, and further ispositioned in the inner portion of the thickened parts 56 and 66. InFIG. 1, the line 73 a indicates a position of the boundary portion 73.In other words, the large diameter portion is inserted to a position(with respect to the upper rotary body) below the apex of the thickenedpart but not below the extension line of the non-projecting portion ofthe plates 51 and 52; the large diameter portion of the lower rotarybody is correspondingly inserted.

[0055] In a case of performing the welding, the frame members 50 and 60are mounted on a bed stand and are fixed thereto. No bed stand exists ata surrounding portion of the thickened part of the lower face. Arotating center of the rotary body 70 is a center of the joining region;namely, such center is a center of the thickness of the plate 54.

[0056] In FIG. 4, a relationship about the dimensions of the respectiveportions will be explained. A width W1 of an apex of the two thickenedportions 56 and 66 (two welding portions 56 and 66), in a case where thetwo thickened portions 56 and 66 (two welding portions 56 and 66) areabutted, is larger than a diameter d of the small diameter portion 72but is smaller than a diameter D of the large diameter portion 71.

[0057] A width W2 of the basis portion of the two thickened portions 56and 66 (two welding portions 56 and 66) is larger than the diameter D ofthe large diameter portion 71. A height Hl of the two thickened portions56 and 66 (two welding portions 56 and 66) is longer than a length ofthe small diameter portion 72.

[0058] When a lower end of the large diameter portion 71 is positionedat the position 73 a of the two thickened portions 56 and 66 (twowelding portions 56 and 66), a tip end of the small diameter portion 72reaches the member 55 or is positioned in the vicinity of the member 55.

[0059]FIG. 2 shows a state in which the friction stir welding has beencompleted. FIG. 2 shows the joining (welding) region W at an upper sideof FIG. 1. The joining region at a lower side is symmetrical with theupper side joining region. At a side of an outer face of the joiningregion W, the dent K is caused, directed toward an inner side of thehollow frame member. At both sides of the dent K there are thick parts56T and 66T.

[0060] The thick parts 56T and 66T are remainders of the thickened parts56 and 66. The thick parts 56T and 66T include matters which areplastically deformed. A bottom face of the dent K is positioned at theouter side portion 73 a, outward from an outer face of the plates 51 and61.

[0061] In a case where the upper side face of FIG. 1 is the outer faceside of the car body of a railway car, an excessive part of the upperface joining region (a part extending outward from the faces of thegeneral portions (non-thickened portions) of the plates 51 and 61)) ismachined by, illustratively, a grinding machine, and it is performed tohave the same plan face as the upper faces of the general portion of theplates 51 and 61. Since the upper face side is machined, it is possibleto carry out easily the cutting working.

[0062] At the lower face side, similarly to the above, the dent K andthe thick parts 56T and 66T exist; however, when they exist at the innerface side of the car body, because they are covered by make-up plates itis unnecessary to machine them.

[0063]FIG. 3 shows a state in which the frame members 50 and 60 mountedon a bed stand 111 are joined through the upper side and the lower side,and next under a state in which they are mounted on the bed stand 111,the upper face side thick parts 56T and 66T have been machined.

[0064] According to the above structure, an occurrence of the dent Kextending to a level below the level of the faces of the generalportions (non-thickened portions) of the plates 51 and 61 can beprevented substantially. As a result, it is not necessary to carry outpadding welding and mending using the putty member.

[0065] Further, in the above-stated embodiment, the end portions 56 aand 66 a of the thickened parts 56 and 66 contact each other; however,in a case where a gap exists between the thickened parts, the base metalof the thickened parts 56 and 66 which has been fluidized under thefriction stir welding is pushed into the gap. As a result, in a case ofan existence of the gap, a default is not generated in the joiningregion.

[0066] Concretely, when the height of the thickened part (H1 in FIG. 4)is 1 mm, two members having a gap of 1 mm therebetween can be joinedwithout default. Further, it is possible to position the dent K outsideof an extension line of the outer face of the plates 51, 52 and 61, 62.Namely, the occurrence of the dent extending beyond the faces of theplates 51, 52 and 61, 62 can be prevented substantially and easily.

[0067] As seen in the foregoing, according to the present invention thetwo members to be joined can be in contact with each other, but need notbe in contact; there can be a gap between the ends of the two members tobe joined. Throughout the present disclosure, where it is described thatthe two members to be joined are adjacent (abutting) each other, the twomembers can be in contact or can have small gaps therebetween.

[0068] Illustratively, the width W2 of the basis portions of thethickened parts 56 and 66 is larger than a diameter D of the largediameter portion 71. The width W1 of the apex of the thickened parts 56and 66 is larger than a diameter d of the small diameter portion 72.When the center of the rotary body 70 is shifted from the center of thethickened parts 56 and 66, the above-stated dimensions are determinedunder a consideration of the gap of the two frame members.

[0069] Further, the thickened parts 56 and 66 of the joining region,when joined, can have a trapezoid shape; in comparison with a case wherethe thickened parts 56 and 66 are extruded with four-sided shapes, inthe present invention no excessive part exists. As a result, the presentinvention can dispense with a small amount of the hollow frame member,and further it is possible to lessen the manufacturing cost.

[0070] Further, it is possible to lessen the machining amount by thegrinding machine, since, e.g., only remaining portions of the thickenedparts need be machined. Further, as shown in FIG. 6, after sides 51 aand 61 a of the thickened parts 56 and 66 are stood up a little from theouter faces of the non-thickened portions of the plates 51 and 61, it ispossible to provide the trapezoid shapes to the thickened portions 56and 66.

[0071] The plate 54 prevents the plates 51 and 61 from bending at thethickened parts 56 and 66, toward the inner side, due to the compressiveforce caused by the rotary bodies 70 and 70.

[0072] In FIG. 1, the right-end shape structure of the hollow framemember 50 may employ the left-end shape structure of the hollow framemember and also may employ the right-end shape structure of the hollowframe member 60. The shape structure of the hollow frame member 60 canemploy similar structure. In a word, it is preferable to joint the twohollow frame members.

[0073] The rotary body 70 is moved by detecting the abutting portionusing an optical sensor. By detecting the slope faces 56 c and 66 c ofthe thickened parts 56 and 66, the position in the width direction ofthe rotary body 70 is determined. As shown in FIG. 7, the slope faces 56n and 66 nm for sensing can be provided at a part to which the thickenedparts 56 m and 66 m are opposite. The slope face 56 n (66 n) can beprovided respectively to both of the thickened parts 56 m and 66 m orcan be provided to one of the thickened parts 56 m and 66 m.

[0074] In each of the above-stated embodiments, the two end faces 56 aand 66 a of the two joining regions are parallel to the axis center ofthe rotary body 70; however, the two end faces 56 a and 66 a can beinclined against the axis center of the rotary body 70. For example, theend face 56 a of one member 50 is inclined and against to this end face56 a the end face 66 a of another member 60 can be overlapped at theupper side.

[0075] According to this structure, even when the gap between the twoend faces is large, according to the rotation of the rotary body 70 itis possible to prevent the outflow of the fluidized metal from theextruded member 55. This structure is suitable to the connection ofmutual pipes.

[0076] A joining apparatus will be explained referring to FIG. 8A. Thehollow frame members 50 and 60 are mounted on the bed stands 111, 111and fixed by a cramp 113. The abutting portions of the two hollow framemembers 50 and 60 are temporarily welded suitably.

[0077] An upper side rotary body 70 is hung down from a running body 121which is run toward a width direction. The running body 121 is movedalong an upper portion frame of a gate type running body 122. Therunning body 122 is run along a rail 123 which is arranged to bothsides, along a longitudinal direction, of the hollow frame members 50and 60.

[0078] A lower side rotary body 70 is provided on a running body 131which is arranged between two seats 111 and 111. The running body 131 ismounted on the running body 132 and is moved toward the width direction.

[0079] The running body 132 is run along the rail 133 and also along thelongitudinal direction of the hollow frame members 50 and 60. The lowerside rotary body 70 is provided on a lower portion of the upper siderotary body 70. The running bodies 121 and 131 also move the rotarybodies 70 and 70 in the vertical direction.

[0080] Plural rollers 124 and 134 for pressing the hollow frame members50 and 60 are provided on the running bodies 121 and 131. The rollers124 and 134 are arranged at a front portion of the rotary bodies 70 and70 and on both sides of the thickened parts 56 and 66. The rollers 124and 134 are provided with plural rows along the running direction asoccasion demands. Rollers can be added in front of and to the rear ofthe rotary body 70.

[0081] The running bodies 121 and 131 have a sensor (not shown in thefigure) which can detect the position to be joined. The running bodies121 and 131 are moved in the width direction by the sensor. In a case alaser is used as the sensor, the slope faces 56 c, 56 c and 66 c, 66 care found and a center to be joined is detected.

[0082] After the joining of the upper face and the lower face of thehollow frame members 50 and 60 using the rotary bodies 70 and 70, andunder a state in which the hollow frame members 50 and 60 are mounted onthe bed stands 111 and 111, the hollow frame members 50 and 60 arefinished smoothly by machining off the thick parts of the upper face.

[0083] When the machining grinding working is carried out by a manualworking, it can be finished more smoothly. For this reason, it ispossible to put on at the upper face the thick part for carrying out themachining working.

[0084] Further, first of all, since the thick part is machined leaving alittle using the machine, and after that the remaining thick part ismachined by manual working, it is possible to shorten the cuttingworking. In this case the rotary body 70 leaves a rear portion ofrunning body 121 unoccupied, and the cutting tool is provided on therunning body 121. And in a case where the rotary body 70 is rotated, thecutting tool carries out the cutting working.

[0085] For example, as shown in FIGS. 8B and 8C, to the rear of therotary body 70 of the upper face side, an end milling machine 126 isprovided on the upper face side running body 121. The end millingmachine 126 cuts off the thick parts 56T and 66T. A lower end of the endmilling machine 126 is positioned at an upper portion a little from theupper faces of the upper face plates 51 and 61 of the hollow framemembers 50 and 60. A diameter of the end milling machine 126 issufficiently larger than the widths of the thick parts 56T and 66T whichare positioned at the above-stated position. The rollers 124 and 134push down a vicinity of the end milling machine 126 from an upperportion and a lower portion and therefore a cutting amount by the endmilling machine 126 is made uniformly.

[0086] In the above-stated embodiments, a pair of the hollow framemembers have respectively the thickened parts at the end portions;however, as shown in FIG. 8D, it is possible to constitute a case whereonly one of the hollow frame members has a thickened part. A metal ofthe thickened part 66 is moved at a clearance between the hollow framemembers 50 and 60 and an upper face of the plate of the hollow framemember 50. Further, similarly to the above, in one hollow frame member60 the thickened part is formed at the upper face plate 61, and inanother hollow frame member 50 the lower face 52 has the thickened part.

[0087] In the above-stated embodiments, the frame member (e.g., anextruded frame member) is exemplified as a hollow frame member; however,it is possible to apply the present invention to a non-hollow, e.g.,extruded, frame member. Hereinafter, such embodiments will be explained.

[0088]FIG. 9 shows an example of a joint structure which has thethickened parts 34 and 35 at the end portions of the plate-shapeextruded frame members 31 and 32, and the frame members 31 and 32 arejoined by abutting the thick parts 34 and 35 to each other and frictionstir welding. During the welding, the extruded frame members 31 and 32are arranged on backing tools (bed stands) 36. To prevent the backingtools from joining with the joining region W, those backing tools 36 aremade of materials harder than the materials of the extruded framemembers 31 and 32.

[0089] Along to the abutting face of this joint, since the rotary body70 is rotated and moved, then the joining region W shown in FIG. 10 canbe obtained. The conditions for the rotary body 70 against the thickenedparts 34 and 35 are similar to those of the above-stated embodiments.

[0090] Next, as shown in FIG. 11, the dent K and the thick parts areremoved smoothly using the grinding machine, etc. The roller 124, etc.,of the joining apparatus is similar to those of the above-statedembodiments.

[0091] Further, in a case where the extruded frame member, etc., hasonly one joining region, in the embodiment shown in FIG. 8A, in place ofthe lower side rotary body 70, a roll for supporting the extruded framemember can be arranged. With this structure, it is unnecessary tosupport a whole face of the frame members 31 and 32; as a result the bedstand structure can be simplified.

[0092] An embodiment shown from FIG. 12 to FIG. 14 shows a case whereone face of each of the frame members 37 and 38 has plural ribs 39; andat an opposed face to the face having the ribs 39 the extruded framemembers 37 and 38, having the thickened parts 34 b and 35 b, are joinedby friction stir welding. The bed stand 36B mounts the lower ends of theribs 39 and the lower faces of the thickened parts 34 and 35. Thefriction stir welding is performed similarly to the above-statedembodiments.

[0093] An embodiment shown from FIG. 15 to FIG. 16 shows a case wherethe extruded frame members 37 c and 38 c, having the thickened parts 34b and 35 b, are provided at a side of the ribs 39. With this structure,a side of a bed stand 36C becomes flat.

[0094] As a result, in a case where at the opposite side of the ribs 39a little unevenness is permitted, it is possible to delete the finishingprocess for making the joining smooth, so that the joined structure canbe manufactured at a low cost. The joining region W is a good joiningregion and a predetermined thickness thereof can be obtained.

[0095] One embodiment shown from FIG. 17 to FIG. 19 will be explained.In FIG. 17, a side structure body 416 of a railway vehicle is comprisedof plural extruded frame members 150 and 160. Each of the extruded framemembers 150 and 150 between an entrance and exit port 171 and a window172, and between the window 172 and the window 172, extend in alongitudinal direction in FIG. 17 (that is, have their length extendingin this longitudinal direction). Each of the extruded frame members 160and 160 at the lower portions of the window 172 and at the upperportions of the window 172 extend in a lateral direction in FIG. 17(that is, have their length extending in this lateral direction).Namely, the extruded frame members 150 and the extruded frame members160 extend in directions (that is, have their lengths) orthogonal toeach other.

[0096] The extruded frame members 150 and 150, which extend in (havetheir lengths extending in) the same direction, are joined to eachother, and the extruded frame members 160 and 160, which extend in (havetheir lengths extending in) the same direction, are joined to eachother, by providing the thickened parts, similarly to the above-statedembodiments.

[0097] An intersecting portion of the directions that the frame members150 and 160 extend is shown in FIG. 18. FIG. 18 shows a condition beforethe friction stir welding. The extruded frame members 150 and 160 have arib 153 and a rib 163 at one side of the plates. The extruded framemembers 150 and 160 are not the hollow frame members. The extruded framemembers 150 and 160 mount the plate 151 and the plate 161 on a bed stand36C. The ribs 153 and 163 direct toward the upper portions. The sides ofthe ribs 153 and 163 are the inner side of the car, and the sides of theplates 151 and 161 are the outer side of the car.

[0098] The end portion of the extruded frame member 150 is extruded to aside of the rib 153 and constitutes a thickened part 156. The thickenedpart 156 is extruded further toward the extruded frame member 160 to bewelded and constitutes an extruded part 157. The extruded part 157 isoverlapped with an inner side of the plate 161 of the extruded framemember 160 (the side of the rib 163). The rib 163 of the part of theextruded part 157 is cut off and removed. Illustratively, an extrudedamount L2 of the extruded part 157 is the same as a width L1 of thethickened part 156. Namely, the extruded part 157 corresponds to thethickened part 156. A tip portion of the extruded part 157 has anoblique side surface similarly to that of the thickened part 156.

[0099] By inserting the rotary body 70 from an upper portion, when thefriction stir welding is carried out, since the extruded part 157 existsoverlying a clearance 150 c between the end portions 150 b and 160 b ofthe two extruded frame members 150 and 160, the metal of the extrudedpart 157, etc., is supplied to the clearance 150 c. Further, the metalis supplied also to the upper portion of the extruded frame member 160.As a result, in a case of the comparison with structure which did nothave the thickened part 156 and the extruded part 157, and further incomparison with structure which did not have only the extruded part 157,in this case a good welding can be obtained.

[0100] Since by cutting off the rib 163 of the extruded frame member 160and the extruded frame member 160 is overlapped by the extruded part157, the plate 161 at the vicinity of the extruded part 157 can bepressed down, and a good welding can be obtained.

[0101] A triangular-shaped groove 158 is provided at an outer face ofthe thickened part 156 which is positioned between the end portion 150 bof the extruded frame member 150 and the end portion 160 b of theextruded frame member 160. This groove 158 works a role of a positionalmark for determining initially the position of the rotary body 70. Thisgroove 158 further works a role of a mark for the sensor.

[0102]FIG. 20 shows a case where the thickened part 156 and the extrudedpart 157 are not provided at the side of the rib 153. The ribs 153 and163 are mounted on a bed stand 36B. The thickened part 156, the extrudedpart 157 and the plates 151 and 161 surrounding these parts are mountedon a bed stand which projects toward an upper portion from the stand36B. The rib 163 at the vicinity of the end portion of the extrudedframe member 160 is cut off. The thickened part 156 and the extrudedpart 157 of the extruded frame member 150 are positioned at the side ofthe plate 151 (the outer face side of the car).

[0103] In a case of the welding of the extruded frame members in whichthe extruded direction is orthogonal, it is possible to use structurehaving only the thickened part 156 and not the extruded part 157.Further, the provision of the extruded part toward the adjacent membercan be adapted to the hollow extruded frame member, etc. Further, theprovision of the extruded part can be adapted to joining two extrudedframe members which are not orthogonal, namely, to the welding of twoparallel members.

[0104] The above method can be adopted to mutual honeycomb panels. Eachhoneycomb panel comprises two face plates, a honeycomb core memberarranged between the two face plates, and a flange member arranged at asurrounding portion of the core member, etc.

[0105] The object matter to be joined can be pipes, etc. In this case,the plate of the above-stated embodiments will be replaced with acylinder suitably.

[0106] Through use of the present invention, dents extending below thesurfaces of the joined members can be avoided. Therefore, finishing ofthe joined members, to provide a smooth surface extending across thejoint between the joined members, can be simplified.

[0107] Furthermore, even when there is a gap (or gaps) between themembers to be joined by the friction stir welding and these gaps arelarge, dents extending below the surfaces of the joined members can beavoided, simplifying finishing work in providing a smooth surfaceextending across the joint.

[0108] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristic thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A structural body, comprising two extruded framemembers friction stir welded to each other, wherein: one side face ofeach of the two extruded frame members is abutted to each other, formingan abutted portion, to form substantially a same face; said abuttedportion is welded from a side of said one side face by friction stirwelding; a protrusion portion which protrudes from said one side face isprovided at a welding portion according to the friction stir welding, toone side face of said two extruded frame members; and said protrusionportion is provided in advance to said one side face of said twoextruded frame members.
 2. A structural body according to claim 1,wherein: each of said two extruded frame members has a rib respectively;said rib is provided on a side of said protrusion portion; and in one ofsaid two extruded frame members, said rib at the vicinity of saidwelding portion is removed by cutting off said rib.
 3. A structural bodyaccording to claim 1, wherein extruded directions of said two extrudedframe members are arranged substantially orthogonally to each other. 4.A car body, comprising two extruded frame members friction stir weldedto each other, wherein: one side face of each of the two extruded framemembers is abutted to each other, forming an abutted portion, to formsubstantially a same face; said abutted portion is welded from a side ofsaid one side face by friction stir welding; a protrusion portion whichprotrudes from said one side face is provided at said welding portionaccording to the friction stir welding, to one of said two extrudedframe members; said protrusion portion is provided in advance to one ofsaid two extruded frame members; a structural body formed by the twoextruded frame members friction stir welded to each other is used as aside structure member for constituting the car body; and said protrusionportion is installed so as to be directed towards a side of an innerface of the car body.
 5. A car body according to claim 4, wherein anextruded direction of said one of said two extruded frame members isorthogonal to an extruded direction of the other of said two extrudedframe members.
 6. A structural body, comprising two extruded framemembers friction stir welded to each other, wherein: one side face ofeach of the two extruded frame members is abutted to each other formingan abutted portion; said abutted portion is welded from a side of saidone side face by friction stir welding; a protrusion portion whichprotrudes in a thickness direction of the two extruded frame members,from said one side face, is provided at a welding portion according tothe friction stir welding, to said one side face of one of the twoextruded frame members, said protrusion portion extending so as tooverlap said one side face of the other of the two extruded framemembers at said welding portion; and said protrusion portion is providedin advance to said one side face of one of the two extruded framemembers.
 7. A structural body according to claim 6, wherein extrudeddirections of said two extruded frame members are arranged substantiallyorthogonally to each other.
 8. A structural body according to claim 6,wherein at least one of the two extruded frame members is an extrudedhollow frame member.
 9. A structural body according to claim 8, whereinboth of said two extruded frame members are extruded hollow framemembers.
 10. A structural body according to claim 6, wherein: each ofthe two extruded frame members includes a second side face opposite saidone side face; said second side face of each of the two extruded framemembers is abutted to each other, at said abutted portion; said abuttedportion is also welded from a side of said second side face by frictionstir welding; another protrusion portion which protrudes in a thicknessdirection from said second side face, is provided at another weldingportion according to the friction stir welding, to said second side faceof one of the two extruded frame members, said another protrusionportion extending so as to overlap said one side face of the other ofthe two extruded frame members at said another welding portion; and saidanother protrusion portion is provided in advance to said second sideface of one of the two extruded frame members.
 11. A structural bodyaccording to claim 10, wherein extruded directions of said two extrudedframe members are arranged substantially orthogonally to each other. 12.A structural body according to claim 11, wherein at least one of the twoextruded frame members is an extruded hollow frame member.
 13. Astructural body according to claim 10, wherein said one side face of thetwo extruded frame members, when forming the abutted portion, formssubstantially a same face; and said second side face of the two extrudedframe members, when forming the abutted portion, forms substantially asame face.
 14. A structural body according to claim 6, wherein said oneside face of the two extruded frame members, when forming the abuttedportion, forms substantially a same face.